Add a fast-path for independent inherited properties

third_party/WebKit/Source/core/style/ComputedStyle.cpp

Index: third_party/WebKit/Source/core/style/ComputedStyle.cpp
diff --git a/third_party/WebKit/Source/core/style/ComputedStyle.cpp b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
index b0b2204dec5d9fe9f107349381a05cb29b66ccee..bcae818fc14c33897e17ee2d142165df0d94e7d3 100644
--- a/third_party/WebKit/Source/core/style/ComputedStyle.cpp
+++ b/third_party/WebKit/Source/core/style/ComputedStyle.cpp
@@ -76,6 +76,10 @@ struct SameSizeAsComputedStyle : public RefCounted<SameSizeAsComputedStyle> {
     struct NonInheritedData {
         unsigned m_bitfields[3];
     } m_nonInheritedData;
+
+    struct IsInheritedFlags {
+        unsigned m_bitfields[1];
+    } m_isInheritedFlags;
 };
 
 static_assert(sizeof(ComputedStyle) == sizeof(SameSizeAsComputedStyle), "ComputedStyle should stay small");
@@ -160,6 +164,7 @@ ALWAYS_INLINE ComputedStyle::ComputedStyle(const ComputedStyle& o)
     , m_svgStyle(o.m_svgStyle)
     , m_inheritedData(o.m_inheritedData)
     , m_nonInheritedData(o.m_nonInheritedData)
+    , m_isInheritedFlags(o.m_isInheritedFlags)
 {
 }
 
@@ -197,6 +202,11 @@ StyleRecalcChange ComputedStyle::stylePropagationDiff(const ComputedStyle* oldSt
         || oldStyle->justifyItems() != newStyle->justifyItems()) // TODO (lajava): We must avoid this Reattach.
         return Reattach;
 
+    if (!oldStyle->independentInheritedEqual(*newStyle)
+        && oldStyle->nonIndependentInheritedEqual(*newStyle)
+        && !oldStyle->hasExplicitlyInheritedProperties())
+        return IndependentInherit;
+
     if (!oldStyle->inheritedEqual(*newStyle)
         || !oldStyle->loadingCustomFontsEqual(*newStyle))
         return Inherit;
@@ -210,6 +220,15 @@ StyleRecalcChange ComputedStyle::stylePropagationDiff(const ComputedStyle* oldSt
     return NoInherit;
 }
 
+// TODO(sashab): Generate this function.
+void ComputedStyle::propagateIndependentInheritedProperties(const ComputedStyle& parent, ComputedStyle& child)
+{
+    if (child.m_isInheritedFlags.m_isPointerEventsInherited)
+        child.setPointerEvents(parent.pointerEvents());
+    if (child.m_isInheritedFlags.m_isVisibilityInherited)
+        child.setVisibility(parent.visibility());
+}
+
 ItemPosition ComputedStyle::resolveAlignment(const ComputedStyle& parentStyle, const ComputedStyle& childStyle, ItemPosition resolvedAutoPositionForLayoutObject)
 {
     // The auto keyword computes to the parent's align-items computed value, or to "stretch", if not set or "auto".
@@ -341,6 +360,10 @@ void ComputedStyle::copyNonInheritedFromCached(const ComputedStyle& other)
     // m_nonInheritedData.m_affectedByDrag
     // m_nonInheritedData.m_isLink
 
+    // Any properties that are inherited on a style are also inherited on elements
+    // that share this style.
+    m_isInheritedFlags = other.m_isInheritedFlags;
+
     if (m_svgStyle != other.m_svgStyle)
         m_svgStyle.access()->copyNonInheritedFromCached(other.m_svgStyle.get());
     DCHECK_EQ(zoom(), initialZoom());
@@ -420,7 +443,18 @@ void ComputedStyle::removeCachedPseudoStyle(PseudoId pid)
 
 bool ComputedStyle::inheritedEqual(const ComputedStyle& other) const
 {
-    return m_inheritedData == other.m_inheritedData
+    return independentInheritedEqual(other)
+        && nonIndependentInheritedEqual(other);
+}
+
+bool ComputedStyle::independentInheritedEqual(const ComputedStyle& other) const
+{
+    return m_inheritedData.compareEqualIndependent(other.m_inheritedData);
+}
+
+bool ComputedStyle::nonIndependentInheritedEqual(const ComputedStyle& other) const
+{
+    return m_inheritedData.compareEqualNonIndependent(other.m_inheritedData)
         && m_styleInheritedData == other.m_styleInheritedData
         && m_svgStyle->inheritedEqual(*other.m_svgStyle)
         && m_rareInheritedData == other.m_rareInheritedData;